I have created a RESTFUL webservice, witch returns a json, but at this time i only consult and show a simple select * , i need to create a complete CRUD solution, if anyone have some samples to share, i'll appreciate.
Best Regards to all
My code until now are:
DAO - Access.java
package dao;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import dto.Usuarios;
public class Access
{
public ArrayList<Usuarios> getUsuarios(Connection con) throws SQLException
{
ArrayList<Usuarios> usuariosList = new ArrayList<Usuarios>();
PreparedStatement stmt = con.prepareStatement("SELECT * FROM usuarios");
ResultSet rs = stmt.executeQuery();
try
{
while(rs.next())
{
Usuarios usuariosObj = new Usuarios();
usuariosObj.setUsr_id(rs.getInt("usr_id"));
usuariosObj.setUsr_login(rs.getString("usr_login"));
usuariosObj.setUsr_pwd(rs.getString("usr_pwd"));
usuariosList.add(usuariosObj);
}
} catch (SQLException e)
{
e.printStackTrace();
}
return usuariosList;
}
}
DTO - Usuarios.java
package dto;
public class Usuarios
{
private int usr_id;
private String usr_login;
private String usr_pwd;
public Usuarios()
{
}
public Usuarios(int usr_id, String usr_login, String usr_pwd)
{
super();
this.usr_id = usr_id;
this.usr_login = usr_login;
this.usr_pwd = usr_pwd;
}
public int getUsr_id()
{
return usr_id;
}
public void setUsr_id(int usr_id)
{
this.usr_id = usr_id;
}
public String getUsr_login()
{
return usr_login;
}
public void setUsr_login(String usr_login)
{
this.usr_login = usr_login;
}
public String getUsr_pwd()
{
return usr_pwd;
}
public void setUsr_pwd(String usr_pwd)
{
this.usr_pwd = usr_pwd;
}
#Override
public String toString()
{
return "[ {usr_id=" + usr_id + ", usr_login=" + usr_login + ", usr_pwd=" + usr_pwd + "} ]";
}
}
Model - AccessManager.java
package model;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.ArrayList;
import dao.Access;
import dao.Database;
import dto.Usuarios;
public class AccessManager
{
public ArrayList<Usuarios> getUsuarios() throws Exception
{
ArrayList<Usuarios> usuariosList = new ArrayList<Usuarios>();
Database db = new Database();
Connection con = db.getConnection();
Access access = new Access();
usuariosList = access.getUsuarios(con);
return usuariosList;
}
}
WebService - UsuariosService.java
package webService;
import java.util.ArrayList;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import com.google.gson.Gson;
import model.AccessManager;
import dto.Usuarios;
#Path("/UsuariosService")
public class UsuariosService
{
#GET
#Path("/usuarios")
#Produces("application/json")
public String usuarios()
{
String usuarios = null;
ArrayList<Usuarios> usuariosList = new ArrayList<Usuarios>();
try
{
usuariosList = new AccessManager().getUsuarios();
Gson gson = new Gson();
//usuarios = gson.toJson(usuariosList);
usuarios = "{\"usuarios\" :" + gson.toJson(usuariosList) + "}";
} catch (Exception e)
{
e.printStackTrace();
}
return usuarios;
}
}
Usually you should ask a specific trouble you have instead of ask for samples. It looks like you have a structured code and all you need is implement all operations exposing as a service.
In case you need a sample, there quite a lot of resources on the web. Something like this: https://code.google.com/p/javaee6-crud-example/
I'll try give you some quick tips below:
WebService - UsuariosService.java
#POST
#Path("/usuarios")
public Response save(Usuario user) {
try {
manager= new AccessManager();
manager.save(user);
return Response.ok("User has been created.").build();
} catch (Exception e) {
e.printStackTrace();
}
return usuarios;
}
#DELETE
#Path("/usuarios/{id}")
public Response delete(#PathParam("id") String id) {
try {
manager= new AccessManager();
manager.delete(id);
return Response.ok("User has been deleted.").build();
} catch (Exception e) {
e.printStackTrace();
}
return usuarios;
}
#PUT
#Path("/usuarios/{id}")
public Response delete(#PathParam("id") String id, Usuario user) {
try {
manager= new AccessManager();
manager.update(id, user);
return Response.ok("User has been updated.").build();
} catch (Exception e) {
e.printStackTrace();
}
return usuarios;
}
If you don´t understand the usage of PUT, DELETE, POST and so on, I recommend you to read HTTP Method Tutorial. There is several discussion regarding this but you might skip it for a while.
I think you might get an idea from here. Your DAO needs to implement methods to perform CRUD interface as well. The link I've added has a very simple sample that might help as well. You might also check this JPA link.
Not sure whether info above helped but I think it is a start since you have to code it in order to understand more about it :)
Related
I don't know if I need more coffee, or my head is tired, but, I feel like an idiot :)
what am I doing wrong???
I want to call the methods within the class but I get complile errors.
Compilation failure: Compilation failure:
java:[35,1] error: illegal start of type
java:[35,21] error: <identifier> expected
java:[35,22] error: ';' expected
I can't execute this block in the class
//this is what doesn't work
if (custkey.contains(",")) {
String[] ck = custkey.split(",");
for ( String k : ck) {
this.loadRefDb(k);
} else {
this.loadRefDb(custkey);
}
}
my class
package com.ge.digital.fleet.dataservice.impl.processor;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.sql.*;
import javax.naming.*;
import javax.sql.*;
import java.sql.*;
import com.ge.digital.fleet.dataservice.impl.db.RefDatabase;
public class RefReplicatedDataProcessor {
private static final Logger log = LoggerFactory.getLogger(RefReplicatedDataProcessor.class);
private RefDatabase refDb = null;
private DataSource dataSource;
private String custkey;
public void setDataSource(DataSource dataSource) {
this.dataSource = dataSource;
}
public void setCustkey(String custkey) {
this.custkey = custkey;
}
public void setRefDatabase(RefDatabase refDb) {
this.refDb = refDb;
}
//this is what doesn't work
if (custkey.contains(",")) {
String[] ck = custkey.split(",");
for ( String k : ck) {
this.loadRefDb(k);
} else {
this.loadRefDb(custkey);
}
}
public void loadRefDb(String custkey) throws SQLException {
log.info("Reference Replicated Data Processor :: start");
refDb.dropDb();
setAssociations(custkey);
refDb.replicationComplete();
log.info("Reference Replicated Data Processor :: Finish");
}
/***
* name: setAssociations(custkey)
* Loads/Builds the cache database with values found in mysql database
*
* returns a List of associations
* G1.DWATT,112-A-001_Gas_Turbine
* G1.ATID,112-A-001_Gas_Turbine
* G1.dvar, 112-A-001_Gas_Turbine
* ...
*/
public void setAssociations(String custkey) throws SQLException {
String reference = "";
String asset = "";
String dbname = "iprcmt1.fleet_associations"; //from old impl database - TODO new database impl
String query = "select reference, asset from " + dbname + " where custkey = ?";
try (Connection conn = dataSource.getConnection();
PreparedStatement stmt = conn.prepareStatement(query)) {
stmt.setString(1, custkey);
try (ResultSet rs = stmt.executeQuery()) {
if (! rs.next() ) {
log.info("SQL Warning ! No associations for key: " + custkey);
} else {
do {
reference = rs.getString(1);
asset = rs.getString(2);
log.info("SQL Associations reference: " + reference + " and asset: " + asset);
refDb.addRow(reference, asset);
} while (rs.next());
}
} catch (Exception ex) {
log.error("SQL Cannot Execute ResultSet Query!");
log.error(ex.getMessage());
}
} catch (Exception e) {
log.error("SQL Cannot Create DataSource Connection! Cannot Create Prepared Statement!");
log.error(e.getMessage());
}
}
}
maybe this ? :)
if (custkey.contains(",")) {
String[] ck = custkey.split(",");
for ( String k : ck) {
this.loadRefDb(k);
}
}else {
this.loadRefDb(custkey);
}
Your code is simply out of place. The code at "//this is what doesn't work" needs to be inside a method or constructor.
public RefReplicatedDataProcessor(){
//this is what didn't work
if (custkey.contains(",")) {
String[] ck = custkey.split(",");
for ( String k : ck) {
this.loadRefDb(k);
}
} else {
this.loadRefDb(custkey);
}
}
Perhaps you should run the split within a method
public void filter(){
if (custkey.contains(",")) {
String[] ck = custkey.split(",");
for ( String k : ck) {
this.loadRefDb(k);
} else {
this.loadRefDb(custkey);
}
}
}
I have created a custom SQLDataset implementation where it takes a SQL query and returns a List of LinkedHashmap back to the requestcontroller to be displayed in JSP or download in Excel format.
Could you please let me know if the approach is thread safe?
SqlDataset.java
package com.sqle.core;
import com.util.QueryProcessor;
import java.io.Serializable;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
public class SqlDataset implements Serializable {
private String query;
private QueryProcessor qp;
private ResultSet rsSet;
private List<LinkedHashMap<String, Object>> rsList = new ArrayList<>();
private ArrayList<String> dataHeader = new ArrayList<>();
public SqlDataset() {}
public SqlDataset(String uquery) {
this.query = uquery;
}
private ResultSet getQueryResult() throws Exception {
qp = new QueryProcessor(query);
this.rsSet = qp.getQueryResultSet();
return this.rsSet;
}
public List<LinkedHashMap<String, Object>> getResult() throws Exception {
return this.getValues(this.getQueryResult());
}
public List<LinkedHashMap<String, Object>> getResult(String query) throws Exception {
this.query = query;
return this.getValues(this.getQueryResult());
}
public int getRowCount() {
return this.rsList.size();
}
public ArrayList getHeaders() {
for (LinkedHashMap<String, Object> aRsList : this.rsList) {
for (Map.Entry<String, Object> dh : aRsList.entrySet()) {
if (!this.dataHeader.contains(dh.getKey()))
this.dataHeader.add(dh.getKey());
}
}
return this.dataHeader;
}
private List<LinkedHashMap<String, Object>> getValues(ResultSet rs) throws SQLException {
ResultSetMetaData rmd = rs.getMetaData();
int columns = rmd.getColumnCount();
while (rs.next()) {
LinkedHashMap<String, Object> row = new LinkedHashMap<>(columns);
for (int i = 1; i <= columns; ++i) {
row.put(rmd.getColumnName(i), rs.getObject(i));
}
this.rsList.add(row);
}
return this.rsList;
}
}
Below is the code written in request controller:
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String act = request.getParameter("act").toLowerCase();
RequestDispatcher rd = request.getRequestDispatcher("sqleditor.jsp");
try {
if (act.equalsIgnoreCase("exec")) {
String uqry = request.getParameter("isql");
if (!uqry.isEmpty()) {
SqlDataset sd = new SqlDataset(uqry);
rslist = sd.getResult();
if (sd.getRowCount() > 0) {
headRow = sd.getHeaders();
request.setAttribute("resHead", headRow);
request.setAttribute("result", rslist);
} else {
throw new NoDataException("No data found to display");
}
} else {
throw new NoDataException("Please enter a query");
}
rd.forward(request, response);
} else if (act.equalsIgnoreCase("excel")) {
String uqry = request.getParameter("isql");
if (!uqry.isEmpty()) {
try {
SqlDataset sd = new SqlDataset();
rslist = sd.getResult(uqry);
if (sd.getRowCount() > 0) {
headRow = sd.getHeaders();
response.reset();
response.setContentType("application/vnd.ms-excel");
response.setHeader("Content-Disposition", "attachment; filename=\"" + FILENAME + "\"");
ExcelWriter ew = new ExcelWriter();
ew.initExcelfile(rslist, headRow, response.getOutputStream());
} else {
throw new NoDataException("No data found to download");
}
} catch (Exception evar1) {
throw new AppException(evar1.getMessage());
}
} else {
throw new NoDataException("Please enter a query");
}
}
} catch (SQLException evar2) {
request.setAttribute("errormsg", evar2.getMessage());
rd.forward(request, response);
} catch (NullPointerException evar3) {
request.setAttribute("errormsg", evar3.getMessage());
rd.forward(request, response);
} catch (Exception evar4) {
request.setAttribute("errormsg", evar4.getMessage());
rd.forward(request, response);
}
}
Will this code work is multiple users use this application and running different queries successively?
Modified SQLdataset class:
package com.sqle.core;
import com.util.QueryProcessor;
import java.io.Serializable;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
public class SqlDataset implements Serializable {
private List<LinkedHashMap<String, Object>> rsList = new ArrayList<>();
public SqlDataset() {}
private ResultSet getQueryResult(String query) throws Exception {
QueryProcessor qp = new QueryProcessor(query);
ResultSet rsSet = qp.getQueryResultSet();
return rsSet;
}
public List<LinkedHashMap<String, Object>> getResult(String query) throws Exception {
return this.getValues(this.getQueryResult(query));
}
public ArrayList getHeaders() {
ArrayList<String> dataHeader = new ArrayList<>();
for (LinkedHashMap<String, Object> aRsList : this.rsList) {
for (Map.Entry<String, Object> dh : aRsList.entrySet()) {
if (!dataHeader.contains(dh.getKey()))
dataHeader.add(dh.getKey());
}
}
return dataHeader;
}
private List<LinkedHashMap<String, Object>> getValues(ResultSet rs) throws SQLException {
ResultSetMetaData rmd = rs.getMetaData();
int columns = rmd.getColumnCount();
while (rs.next()) {
LinkedHashMap<String, Object> row = new LinkedHashMap<>(columns);
for (int i = 1; i <= columns; ++i) {
row.put(rmd.getColumnName(i), rs.getObject(i));
}
this.rsList.add(row);
}
return this.rsList;
}
public int getRowCount() {
return this.rsList.size();
}
}
It depends on how you use this class.
With your doPost method in controller it is thread safe for multiple users because you create new SqlDataset object every time.
It means it will be used only by thread which processes a single request.
Your Controller code is re-entrant and thread safe.
BTW in case if you plan to use your SqlDataset as singleton (e.g. Spring bean or such) - it is not thread safe. It has instance variables used in process - it means SqlDataset methods are not re-entrant.
just think about them...
do you really need private QueryProcessor qp; while you create new instance every time in the getQueryResult() method?
do you really need private ArrayList<String> dataHeader = new ArrayList<>();
while you just return it from getHeaders() - why do not just create new ArrayList before for loops inside the method.
...and so on...
If you make everything passed to methods as parameters and return everything created inside methods it will be fully thread safe.
Singletons may have only immutable instance variables (logically almost constants) to keep some settings or properties applicable to any threads which use it.
The SqlDataset.java itself is not thread safe as you have instance variables in it.
However if you only use it in some of your request controller's methods then there will be no problems. This is because a Servlet is not thread safe but the Servlets methods are that.
I have a RESTful application that connects to MySQL database (raw paste here: https://pastebin.com/raw/3fBp3j0B) and prints out table data in JSON format.
If I System.out.println() some data from ResultSet, everything shows up correctly, but with the JSON API only the last row in the table is printed out, twice.
import java.sql.*;
import javax.json.*;
public class Tietokanta {
protected Connection yhteys = null;
protected Statement kysely = null;
protected ResultSet tulosjoukko = null;
public boolean avaaYhteys() {
boolean ok = true;
try {
Class.forName("com.mysql.cj.jdbc.Driver");
yhteys = DriverManager.getConnection("jdbc:mysql://localhost/savukelaskuri?serverTimezone=UTC", "root", "");
} catch (Exception e) {
e.printStackTrace();
ok = false;
}
return ok;
}
public boolean suljeYhteys() {
boolean ok = true;
try {
this.yhteys.close();
} catch (Exception e) {
ok = false;
}
return ok;
}
}
...
import java.math.BigDecimal;
import javax.json.Json;
import javax.json.JsonArray;
import javax.ws.rs.core.Context;
import javax.ws.rs.core.UriInfo;
import javax.ws.rs.Produces;
import javax.ws.rs.Consumes;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.PUT;
import static javax.ws.rs.client.Entity.json;
import javax.ws.rs.core.MediaType;
import org.json.JSONArray;
import org.json.JSONObject;
#Path("savukkeet")
public class ApiResource extends Tietokanta {
JSONObject jsonolio = new JSONObject();
JSONArray jsontaulu = new JSONArray();
#Context
private UriInfo context;
public ApiResource() {
this.avaaYhteys();
}
#GET
#Produces(MediaType.APPLICATION_JSON)
public String getJson() {
try {
kysely = yhteys.createStatement();
String sql = "SELECT * FROM kulutus";
tulosjoukko = kysely.executeQuery(sql);
while (tulosjoukko.next()) {
System.out.println(tulosjoukko.getString("pvm"));
jsonolio.put("id", tulosjoukko.getInt("id"));
jsonolio.put("pvm", tulosjoukko.getString("pvm"));
jsonolio.put("kulutus", tulosjoukko.getInt("kulutus"));
jsontaulu.put(jsonolio);
}
} catch (Exception e) {
e.printStackTrace();
}
return jsontaulu.toString(4);
}
}
I expect the result to be
[
{
"kulutus": 9,
"pvm": "2019-01-14 16:46:00",
"id": 1
},
{
"kulutus": 8,
"pvm": "2019-01-15 21:18:00",
"id": 2
}
]
but instead I get this
[
{
"kulutus": 8,
"pvm": "2019-01-15 21:18:00",
"id": 2
},
{
"kulutus": 8,
"pvm": "2019-01-15 21:18:00",
"id": 2
}
]
It should work if you create a new JSONObject for each iteration in the while loop:
while (tulosjoukko.next()) {
System.out.println(tulosjoukko.getString("pvm"));
jsonolio = new JSONObject();
jsonolio.put("id", tulosjoukko.getInt("id"));
jsonolio.put("pvm", tulosjoukko.getString("pvm"));
jsonolio.put("kulutus", tulosjoukko.getInt("kulutus"));
jsontaulu.put(jsonolio);
}
Java is pass-by-reference, so when you put a property to jsonolio it overrides the previous value even inside the JSONArray because it is still the same object
putting an object in another container does not make a copy for you. you have 1 json Object and you fill it twice. and you put 2 copies of it in the list. at the end the 1 object just has the second set of values in it. so that is what gets output.
put this line JSONObject jsonolio = new JSONObject(); just after while (tulosjoukko.next()) {
I'm writing a program (Java Application) for reading ePassport. For access I use the library org.jmrtd. What kind of object should I transfer in CardService.getInstance() ?
import net.sf.scuba.smartcards.CardService;
import net.sf.scuba.smartcards.CardServiceException;
import org.jmrtd.BACKeySpec;
import org.jmrtd.PassportService;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class TestComponent {
private static final Logger log = LoggerFactory.getLogger(MainApp.class);
public static void main(String args[]) {
try {
CardService cs = CardService.getInstance(???????);
PassportService ps = new PassportService(cs);
ps.open();
ps.sendSelectApplet(false);
ps.sendSelectApplet(false);
BACKeySpec bacKey = new BACKeySpec() {
public String getDocumentNumber() {
return "xxxxxxxx";
}
public String getDateOfBirth() {
return "yyMMdd";
}
public String getDateOfExpiry() {
return "yyMMdd";
}
};
ps.doBAC(bacKey);
ps.close();
} catch (CardServiceException e) {
e.printStackTrace();
}
}
}
Answer found:
add in pom
net.sf.scuba
scuba-sc-j2se
0.0.13
import net.sf.scuba.smartcards.TerminalCardService;
CardTerminal terminal =TerminalFactory.getDefault().terminals().list().get(0);
CardService cs = CardService.getInstance(terminal);
PassportService ps = new PassportService(cs);
ps.open();
I've recently starting working on a java webapp (JSP / Servlet) that was developed by the internal developer of a company.
This app randomly doesn't return data, and inspecting the log I found some NullPointerExceptions related to the classes' member variable which holds the database connection. Following the stack trace it seems that a second thread closes the connection after it ended its task leaving the first thread without a connection.
By the needs of the company the app uses different databases, one which rules appdata, and others which contain data the app has to retrieve. So every class attached to the main servlet may connect to one or more databases depending on the task it has to accomplish.
I'm not familiar with JavaEE but giving a look at the database connection class, I see nothing which protect threads from conflicting each other.
Which is the correct way to handle such connections?
This is the code of the Database handler:
package it.metmi.mmasgis.utils;
import java.sql.*;
import java.util.ArrayList;
import java.util.HashMap;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
public class DBManager
{
private String szDatabase;
private String szUsername;
private String szPassword;
private String szError;
private Connection db;
private boolean bConnected;
private Logger logger;
public DBManager(String szDBName)
{
this(szDBName, "", "");
}
public DBManager(String szDBName, String szName, String szPass)
{
szDatabase = szDBName;
szUsername = szName;
szPassword = szPass;
bConnected = false;
szError = "";
logger = LogManager.getFormatterLogger(DBManager.class.getName());
}
public boolean connect()
{
logger.entry();
try {
Class.forName("com.mysql.jdbc.Driver");
if(!szDatabase.isEmpty())
{
String szCon = "jdbc:mysql://localhost/" + szDatabase;
if(!szUsername.isEmpty())
{
szCon += "?user=" + szUsername;
if(!szPassword.isEmpty())
szCon += "&password=" + szPassword;
}
db = DriverManager.getConnection(szCon);
bConnected = true;
} else {
logger.error("No database name!!");
System.exit(0);
}
} catch(SQLException | ClassNotFoundException e) {
szError = e.getMessage();
e.printStackTrace();
logger.error("Can't connect: %s", e);
}
return logger.exit(bConnected);
}
public void disconnect()
{
logger.entry();
try {
db.close();
bConnected = false;
} catch(SQLException e) {
e.printStackTrace();
logger.error("Can't disconnect: %s", e);
}
logger.exit();
}
public boolean isConnected()
{
return bConnected;
}
public String getError()
{
return szError;
}
public ArrayList<HashMap<String,String>> query(String szQuery)
{
logger.entry(szQuery);
ArrayList<HashMap<String,String>> aResults = new ArrayList<HashMap<String,String>>();
int iCols = 0;
try {
Statement stmt = db.createStatement();
logger.info("Query: %s", szQuery);
ResultSet rs = stmt.executeQuery(szQuery);
ResultSetMetaData rsmd = rs.getMetaData();
iCols = rsmd.getColumnCount();
while(rs.next())
{
HashMap<String,String> pv = new HashMap<String,String>();
for(int i = 0; i < iCols; i++)
{
String szCol = rsmd.getColumnLabel(i + 1);
String szVal = rs.getString(i + 1);
pv.put(szCol, szVal);
}
aResults.add(pv);
}
rs.close();
stmt.close();
} catch(SQLException e) {
e.printStackTrace();
szError = e.getMessage();
logger.error("Error executing query: %s", e);
}
return logger.exit(aResults);
}
public boolean update(String szQuery)
{
logger.entry(szQuery);
boolean bResult = false;
try {
Statement stmt = db.createStatement();
logger.info("Query: %s", szQuery);
stmt.executeUpdate(szQuery);
bResult = true;
stmt.close();
} catch(SQLException e) {
e.printStackTrace();
szError = e.getMessage();
bResult = false;
logger.error("Error executing query: %s", e);
}
return logger.exit(bResult);
}
}
The class Task which all the servlet classes are based on, is a simple abstract class:
package it.metmi.mmasgis.servlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public abstract class Task
{
public abstract void doTask(HttpServletRequest request, HttpServletResponse response);
}
The class which throws NullPointerExceptions it this one, during the invocation of db.disconnect(). This class is called rapidly via AJAX 4 or 5 times from the interface written in JS.
package it.metmi.mmasgis.servlet.params;
import it.metmi.mmasgis.servlet.Task;
import it.metmi.mmasgis.utils.Const;
import it.metmi.mmasgis.utils.DBManager;
import it.metmi.mmasgis.utils.Query;
import it.metmi.mmasgis.utils.Utility;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.HashMap;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
public class ClassType extends Task
{
private DBManager db = null;
private Logger logger = LogManager.getFormatterLogger(ClassType.class.getName());
#Override
public void doTask(HttpServletRequest request, HttpServletResponse response)
{
logger.entry(request, response);
String szCensimento = Utility.getParameter(request, "censimento");
String szCategoria = Utility.getParameter(request, "category");
ArrayList<HashMap<String,String>> aClasses = new ArrayList<HashMap<String,String>>();
PrintWriter out = null;
logger.debug("Census: %s", szCensimento);
logger.debug("Category: %s", szCategoria);
db = new DBManager(szCensimento, Const.DB_USER, Const.DB_PASS);
if(db.connect())
{
String szQuery = String.format(Query.classes, szCategoria, szCategoria);
aClasses = db.query(szQuery);
db.disconnect();
}
try {
out = response.getWriter();
jsonEncode(aClasses, out);
} catch(IOException e) {
e.printStackTrace();
logger.error("Failed to encode JSON: %s", e);
}
logger.exit();
}
private void jsonEncode(ArrayList<HashMap<String,String>> aData, PrintWriter out)
{
HashMap<String,Object> result = new HashMap<String,Object>();
result.put("results", aData);
result.put("success", true);
Gson gson = new GsonBuilder().create();
gson.toJson(result, out);
}
}
If the webapp would use only one database, it could be rewritten as a Singleton, but in this way I have no idea on how to handle different connections for different databases.
How can avoid these exceptions?
The problem was that the connection object was declared as member.
Moving the variable inside the methods resolved.